Technical Field
The present invention relates to optical waveguides and, more particularly, to a single-mode polymer waveguide connector.
Description of the Related Art
Waveguides are used to transport, e.g., optical signals over large distances with very low losses. Waveguides employ, e.g., a difference between a refractive index for an internal medium called “core” and an external medium called “clad”. In the example of fiber optics, the transport medium “core” is made of a higher refractive index glass and the external medium “clad” is made of a lower refractive index glass. These two glass layers are surrounded by sheath, shielding, or air. When an optical signal in the inner core layer hits the boundary between core and clad, it is internally reflected instead of escaping from core layer. As a result, optical fibers can be used to transport very low-loss signals across long distances.
Optical fibers used for waveguides are thin, flexible, and frequently made of silica glass, but may also be made from, e.g., fluoride glass, phosphate glass, chalcogenide glass, or crystal materials such as sapphire. Appropriate materials are selected in accordance with desired refractive properties. Transmissions over optical fiber suffer from less loss and electromagnetic interference relative to metal wires. In addition, since information propagates through optical fibers at the speed of light, latency is decreased over large distances using optical communications. Some fibers support many transverse transmission modes and are called multi-mode fibers, whereas others support a single mode and are called single-mode fibers. Single-mode fibers are frequently used for long-distance links, as multi-mode fibers are susceptible to modal dispersion over long distances due to slightly different transmission speeds between the different modes.
Polymer materials exhibit favorable properties for use in optical waveguides. Polymers provide good optical properties and are cost effective and easy to fabricate. Polymers are furthermore compatible with printed circuit board manufacturing processes due to a resilience against solder reflow and lamination processes, such that polymer structures can be formed directly on printed circuit boards alongside semiconductor-based components. Polymer waveguides are used for high-density optical interconnects in fiber-optic communications, optronics, and other light-based technologies. Waveguide connectors are used to connect between separate polymer waveguides and between polymer waveguides and glass fibers.
Existing polymer waveguide connectors are difficult to install under precise positioning requirements. One such connector is the polymer mechanical transfer (PMT) connector which is used as a multimode polymer waveguide connector. These connectors are difficult to assemble with positioning errors of under a few micrometers and are simply not feasible for positioning errors of less than a micrometer. Positioning errors can lead to loss of signal from, e.g., reflections that occur at imperfect junctions.
Although efforts have been made to improve positioning for polymer waveguide connectors, difficulties arise in fabrication. The initial positioning error of, e.g., a positioning groove on a waveguide may be under a micrometer due to precise lithography fabrication, but the polymers use generally have high coefficients of thermal expansion (CTEs), which causes the polymer to shrink or expand as the temperature changes.